A fast and efficient method for installing small diameter flowlines and control lines offshore is by means of reel, tensioner, and straightener devices mounted on a floating vessel. However, this "pipe reel" method becomes awkward if multiple lines must be laid simultaneously, as is often the case for flowlines and control lines laid to, or originating at, seafloor wellheads. A typical flowline bundle to such a subsea well consists of production flowlines, annulus access line, chemical injection line, hydraulic power line and electrical control cable. When multiple lines are to be laid in a single bundle, it becomes necessary to spool each line onto a separate reel, and then either (1) lay each line separately off the floating vessel while carefully monitoring each suspended span, or (2) bring the separate lines together and wrap them with tape to form a "flowline bundle" which is then laid into the water as a single entity. Alternately, a flowline bundle may be placed inside a large "carrier pipe" and towed into position, instead of being laid from a vessel.
When lines are brought together and simply wrapped to provide a multiple tube bundle without twisting the tubes, the wrapped bundle has very poor mechanical behavior in bending. The tube bundles cannot be spooled onto reels or pulled through curved conduits such as J-tubes, etc., due to the buckling of the tubes on the inside radius as they are placed in compression. This buckling of the tubes due to bending may be avoided by first winding the tubes into a continuous rope-like set of helixes. For applications requiring bending a bundle of tubes, the helical bundle configuration is therefore highly desirable.
An apparatus for preparing such a helical bundle is disclosed in U.S. Pat. No. 4,843,713. This apparatus is capable of preparing bundles of pipe and tubing by laying out straight lengths of the pipe and tubing, then rotating and translating the end of the bundle after it passes through a special twist head. Alternately, the bundle may be formed by rotating the straight lengths of pipe and tube and simply translating the end of the bundle after passing through the twist head. The sections of helically bundled pipe and tube can then be joined with other helical bundles and rolled onto a reel from which the bundle may be carried offshore and laid.
The apparatus of U.S. Pat. No. '713 can only bundle separate lengths of pipe and tubing which are not longer than the length of the work space available. These limited lengths must then be joined. The resultant connections slow the fabrication process and create discontinuities in the external corrosion coating. It would be preferable to provide an apparatus and method to prepare helically coiled tube bundles wherein spools of tubing could be wound to provide extended lengths of bundles without coupling.
Helically wound tubing bundles are also disclosed in U.S. Pat. Nos. 607,932, 2,832,374, 3,269,422, 3,315,703, 3,400,737, 3,526,086, and 4,256,146, Great Britain Patent Publication Nos. 838,070, 923,816, 1,160,508, 1,210,206, 1,601,122, and 2,038,988, and European Patent Application No. 0 177 475. The cables of these references, with the exception of U.S. Patent No. 607,932, are each strapped or wrapped. The tension and bending stress required to maintain a helical configuration according to the present invention are not suggested or disclosed by any of these references.
U.S. Pat. No. 3,269,422, at column 5, lines 10-19, discloses using a cabling machine to prepare the helically wound bundle. A cabling machine typically has a rotating spindle of spools, from which wires are pulled and twisted together. The length of cables, or twisted tube bundles, which can be prepared without coupling is limited only by the capacity of the spools.
It is therefore an object of the present invention to provide a method and apparatus to prepare helical wound bundles of externally coated metal tubing wherein the bundles do not require strapping to hold the bundles together, and wherein the bundles can be prepared in long lengths without coupling.